[LLVMdev] Troubles with llvm.gcroot and exception handling

Paul Melis llvm at assumetheposition.nl
Wed Dec 2 01:15:47 PST 2009

[Forgot to include llvmdev in my reply, sending a second time]

Hi Duncan,

Duncan Sands wrote:
>> 22:40|melis at juggle2:~/projects/llvm_gc> llc root.ll
>> 22:40|melis at juggle2:~/projects/llvm_gc> gcc -o r root.s
>> /usr/lib/gcc/i686-pc-linux-gnu/4.3.4/../../../../i686-pc-linux-gnu/bin/ld:
>> error in /tmp/ccGhPZDb.o(.eh_frame); no .eh_frame_hdr table will be
>> created.
> the assembler you pasted assembles for me on x86-32 linux.

Ah, sorry for not being clear. The piece of assembler shown was for the
case where the gcroot call was removed and no exception handling code was
generated. I should have included the assembly for root.ll as shown.

>> I'm actually puzzled that exception handling code is generated, and more
>> so that it is caused by the llvm.gcroot call. If I comment that one out
>> all no exception handling stuff is created:
> The EscapeEnumerator code in ShadowStackGC.cpp adds cleanup code using
> invoke and unwind - might be related to this?

Okay, so that's probably where the EH stuff comes from. Does the assembler
error indicate a bug or is there something else I need to do (like using a
gcc flag, or perhaps using ld instead of gcc) to generate an executable?


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